U.S. Pat. No. 4,680,992 issued Jul. 21, 1987 to Hayasaki et al. and JP-A 62-159839 laid open on Jul. 15, 1987 disclose a vehicle drive train owned by the assignee of the present application. This known vehicle drive train includes a torque converter lock-up clutch situated between an engine with a throttle valve that opens in degrees and an input shaft of an automatic transmission. The lock-up clutch is engaged to connect a turbine runner and a pump impeller to each other. Release of engagement of the lock-up clutch enables hydraulic drive between the pump impeller and the turbine runner for torque multiplication and shock reduction upon ratio change in the automatic transmission. If an operator selects a Drive ("D") range position through a selector lever, the automatic transmission operates in automatic ratio change mode. In the automatic ratio change mode, a desired ratio is determined based on vehicle speed and engine load and established by a ratio change actuator in the form of shift solenoids associated with shift valves. The shift valves guide hydraulic fluid under pressure to appropriate one or ones of torque transmitting units, such as friction clutches and brakes, to establish the desired ratio. For saving fuel consumption, a control system engages the lock-up clutch when torque multiplication is not needed in the automatic ratio change mode.
JP-A 8-210492 discloses a control system for a vehicle engine and automatic transmission drive train. This known control system controls engagement of a torque converter lock-up clutch along with a ratio control for improved fuel economy during operation of an automatic transmission in manual ratio change mode. The prior art control systems are fairly well developed. However, a need remains for further development of such control systems, especially in current movement to increasing user satisfaction.